1. Field of the Invention
This invention relates to sensing of electrical signals within a living body. More particularly, this invention relates to sensing of electrical signals within a living body, while tracking an object in the body using impedance measurements.
2. Description of the Related Art
A wide range of medical procedures involve placing objects, such as sensors, tubes, catheters, dispensing devices, and implants, within the body. Position sensing systems have been developed for tracking such objects. For example, U.S. Pat. No. 5,983,126, to Wittkampf, whose disclosure is incorporated herein by reference, describes a system in which catheter position is detected using electrical impedance methods. U.S. Patent Application Publications 2006/0173251, to Govari et al., and 2007/0038078, to Osadchy, which are herein incorporated by reference, describe impedance-based methods for sensing the position of a probe by passing electrical currents through the body between an electrode on the probe and a plurality of locations on a surface of the body.
Systems such as those described above may be used to track the position of a catheter within a patient's heart. A physician may use the catheter, for example, for diagnostic purposes, such as electrophysiology studies, and for therapeutic purposes, such as treating cardiac arrhythmias. In the course of such procedures, the physician may wish to pace the heart, by applying a suitable electrical signal via an electrode at or near the catheter tip. For this purpose, it is common to connect a pacing generator across the same electrodes on the catheter as are used for impedance-based position sensing.